1. Field of the Invention
The present invention is directed to the stacking performance of a catch tray of a stack alignment device for stacking recording sheets on which printing has been performed by an image forming apparatus, and also directed to a sheet discharge device and an image forming apparatus that include the stack alignment device.
2. Description of the Related Art
Such image forming apparatuses are used in a variety of ways, and as a result, are generally required to be capable of accommodating the successive use of sheets of different sizes (for example, from A3 size to A6 size). Sheets of different sizes, on which images have been formed inside an image forming apparatus, are discharged from a discharge outlet of the image forming apparatus and then stacked on a catch tray large enough to hold sheets of normal sizes.
As for such a catch tray, the best known structure is that a downwardly inclined tray is provided below the discharge outlet so as to receive sheets discharged from the image forming apparatus. According to this structure, the leading edge of a first discharged sheet is caught by a stopper provided at the lower end of the catch tray and accordingly, the sheet is placed inside the catch tray. However, it is sometimes the case that the rear edge of a sheet is positioned halfway in the tray along the longitudinal direction.
If multiple sheets are stacked in this manner, the leading edge of a subsequently discharged sheet strikes against the rear end of the stacked group of sheets having an increased thickness, or a preceding sheet is pushed out by a succeeding sheet due to surface friction. As a result, a nicely aligned stack of sheets cannot be obtained.    (Patent Document 1) Japanese Laid-open Patent Application Publication No. H09-208106    (Patent Document 2) Japanese Laid-open Patent Application Publication No. H09-086755    (Patent Document 3) Japanese Patent No. 3373656    (Patent Document 4) Japanese Laid-open Patent Application Publication No. H08-259082    (Patent Document 5) Japanese Patent No. 3744704
The present invention aims at providing a catch tray formed in a simple structure at low cost, which catch tray has a stopper made of a wire rod material or another elastic material for catching the leading edges of transfer sheets, causes no sheet jam, and allows transfer sheets of different sizes to be stacked inside.